Many sheet metal parts are produced by bending the sheet metal with a press brake or similar sheet metal bending machine. Press brakes are also sometimes known in the industry as bending brakes, bending presses or pan brakes. Typically a press brake is a hydraulic press which has a metal die and a metal punch which are shaped to form a particular bend or curve in the sheet metal when the die and punch are pressed together with the sheet metal in-between. Because it involves metal-to-metal contact and because there is often relative movement between the sheet metal and the punch or die, it is not uncommon for there to be die marks or scratches in the surface of the sheet metal from the bending process. For high precision sheet metal parts or for parts that must be visually perfect such as metal cabinets or display cases, it is highly undesirable to have scratches and marks on the parts. Precoated, plated or painted sheet metal is especially susceptible to scratching or marring during the bending process. Also, scratches in the surface can cause problems in the painting or plating process if the parts are painted or plated after bending.
Some sheet metal shops have recognized this problem and have begun using sheets of protective material such as plastic film, canvas or sailcloth between the sheet metal and the punch or die to avoid causing marks. The sheets of protective material must be individually cut and is manually placed on the press brake. This process is tedious and time consuming and it slows down the production of parts. It is also not entirely reliable because the loose sheets of protective material are free to move until the press closes. Consequently, the protective material sometimes shifts, exposing the sheet metal to being scratched or indented by the machine. Because the manual process of cutting and placing the protective material is so time consuming, machine operators may try to use the same sheet of material over and over again without moving or replacing it. If this is done the protective material quickly wears through at the high pressure points, exposing the sheet metal parts to possible damage. It would, therefore, be desirable to provide a system for quickly, reliably and automatically applying protective material to a press brake to prevent scratching and marking of sheet metal during bending operations.